1. Field of the Invention
The present invention relates to an optical disc recording and reproducing apparatus preferable when used for a writable optical disc such as a write once optical disc (CD-R, DVD-R), a rewritable optical disc (CD-RW), and a mini-disc (MD), and a method for reading information.
Specifically, in the present invention, an operation device for operating interference information generated by pre-format addresses in information recording layers adjacent to a target pre-format address is provided. By providing the operation device, the interference information generated by the pre-format addresses adjacent to the target pre-format address at its inner and outer peripheral sides is removed from the read information of the target pre-format address. In this manner, only the information recorded in the target pre-format address can be read. At the same time, even if the light beam is applied across the adjacent information recording layers in accordance with the increase in a storage density of the optical disc, the occurrence of crosstalk can be prevented.
2. Description of the Related Art
In recent years, as information media for editing and recording audio information in such a manner as to suit the preferences of listeners, writable optical discs such as write once optical discs (CD-R, DVD-R), rewritable optical discs (CD-RW), and mini-disc (MD) standardized in ISO/IEC13490-1 are increasingly used. In each of these optical discs 10, as shown in FIG. 1A, grooves 1 for guiding a light beam (hereinafter, referred to as pregrooves) are formed, and a positioning method referred to as a tracking servo is employed. The tracking servo is a mechanism where pits and projections constituting lands 2 formed on both sides of each pregroove 1 are detected to decide the position of an optical pickup, so that the desired pregroove 1 is accurately irradiated with a laser beam.
Sloped surfaces of the land, which coincide to both side surfaces of the pregroove 1, is formed with a slight wobble in the form of sine wave in-phase with each other as shown in FIG. 1B. The wobble signal indicating the wobble component has been subjected to FM modulation. In the wobble signal, time axis information which indicates the position on the optical disc 10, and a recommended value of the power of the laser beam optimum for recording are encoded.
This time axis information is referred to as ATIP (absolute time in pregroove) information, and is written as an absolute time information in the signal recording region (i.e. a program region) of the optical disc 10 along a direction from the starting point at its inner peripheral side toward its outer peripheral side. The ATIP information is written in the processing of the CD-R and CD-RW. The ATIP information is written in the optical disc 10 such as CD-R, CD-RW, and MD-R in a modulation method referred to as bi-phase modulation mode. In this mode, a baseband modulation is conducted where, depending on whether the waveform of the last pulse signal constituting the error correction information of the immediately preceding pre-format address ends at a high level or low level, the pre-format address in the next frame is connected without being inverted, or the pre-format address is inverted and connected.
The ATIP information is written, for example, in the side surfaces Us, Ut of the pregroove 1 between two lands 2a, 2b shown in FIG. 1B. That is, the ATIP information is written in the side surface Us of the land 2a located at the inner peripheral side of the pregroove 1 in which data is recorded, and in the side surface Ut of the land 2b located at the outer peripheral side of the pregroove 1 in such a manner that the ATIP information written in the side surface Us is synchronous to the ATIP information written in the side surface Ut.
Therefore, the ATIP information can be read as a wobble signal by detecting the reflected light from the main spot 4 on the wobble formed in the lands 2a, 2b by two light receiving elements split in the direction of track. The preceding side spot 3 is a light beam preceding the main spot 4 which is a light beam used for recording information. The broken line circles in FIG. 1B show spot diameters of the light beam applied to the optical disc having a standard density. The two-dot long and two short dashes line circles show a light beam of which irradiation diameter is relatively enlarged as the pregrooves are formed so as to be closer to each other in accordance with the increase in a storage density of the optical disc 10. This problem arises because there is a limitation on enlarging the spot diameters of the light beam.
The wobble formed in the land 2a located at the inner peripheral side is detected as a wobble signal by the posterior side spot 5. The wobble signal is produced in such a manner that its center frequency becomes 22.05 kHz for example, when the optical disc 10 is rotated at a standard velocity (CLV) of a compact disc (CD). One sector of the ATIP information is constituted in such a manner as to coincide to one data sector after the signal is recorded. Therefore, at the time of recording information, the pregrooves 1 are irradiated with a light beam with a predetermined intensity and information is written therein while the sector of the ATIP information is synchronous with the data sector.
In a conventional method for reading information, if information is read based on the pre-format addresses which are written in the bi-phase modulation mode as it is without conducting any processing in the recent situation where the lands 2a, 2b are arranged at narrower pitches (hereinafter, also referred to as track pitches in some cases) P in accordance with the increase in the storage density of the optical disc 10, the light beam of which irradiation diameter is relatively enlarged as the pregrooves 1 are formed so as to be closer to each other is applied across the adjacent pregrooves 1 (see FIG. 1B).
In other words, even if the main spot 4 is in the shape of a complete circle, when the spot diameter is larger than the track pitches P, a leakage from the adjacent track occurs. In this case, there is much fear that a crosstalk is generated. The crosstalk causes a phase modulation to create jitter, and as a result, the signal-noise (S/N) ratio is lowered.
As a result, when the bi-phase signal constituting the target pre-format address at the reading point is superposed onto the bi-phase signal of the other pre-format address adjacent to the target pre-format address, there arises a problem that the phase difference therebetween is large, and larger jitter is created as the period of the high-level is shorter.
In addition, if it is attempted to obtain time axis information by use of the return light from the main spot 4 while forming the pit 61 in the main spot 4, a high speed AGC and a divider are required, and the structure of the apparatus becomes complicated. When the signal is written at a speed higher than a standard speed, the light amount of return light is fluctuated by the influence of the formation of pit, even if the power of the laser beam is lowered from the signal writing level to the signal reading level by sampling and holding the signal. In this case, there is a fear that the time axis information cannot be read accurately.
The present invention has been conducted to solve the above-described problems of the prior arts, and the objective thereof is to provide an optical disc recording and reproducing apparatus from which the target pre-format address and the recorded information can be read with excellent reproducibility, as well as being capable of preventing the occurrence of crosstalk in adjacent pregrooves, even if a light beam is applied across adjacent information recording layers in accordance with the increase in the storage density of the optical disc, and a method for reading information.
The above-described problems can be solved by an optical disc reproducing apparatus for reading information from an optical disc formed with addresses beforehand, and into which information has been recorded based on the addresses. And the optical disc reproducing apparatus includes: an information reading device for emitting a light beam to an optical disc, so as to read a target address and recorded information from the optical disc and to output the read information; and an operation device for operating the addresses adjacent to the target address, which has been input from the information reading device, at its inner and outer peripheral sides, and after that for operating interference information generated by the addresses adjacent to the target address at its inner and outer peripheral sides to subtract the interference information from the read information of the target address.
According to an optical disc reproducing apparatus of present information, when information is read from the optical disc into which the information has been recorded based on the addresses, the optical disc is irradiated with a light beam, so as to read the target address and the recorded information from the optical disc by the information reading device. Then, the read information is output to the operation device. In the operation device, the addresses adjacent to the target address at its inner and outer peripheral sides are operated based on the read information, so as to operate the interference information generated by the addresses adjacent to the target address at its inner and outer peripheral sides. After that, the interference information is subtracted from the read information of the target address.
Accordingly, the interference information by the pre-format addresses adjacent to the target pre-format address at its inner and outer peripheral sides is removed from the information read from the optical disc, and whereby only the information recorded in the target pre-format address can be taken out. As a result, even if the light beam is applied across the information recording layers adjacent to each other in accordance with the increase in the recording density of the optical disc, the occurrence of crosstalk can be prevented.
According to a method for reading information of the present invention, information is read from an optical disc having addresses formed beforehand, and the information has been recorded in the optical disc based on the addresses. And the optical disc is irradiated with a light beam, so as to read the target address and the recorded information from the optical disc to obtain read information. Based on thus-obtained read information, the addresses adjacent to the target address at its inner and outer peripheral sides are operated, and then the interference information generated by the addresses adjacent to the target address at its inner and outer peripheral sides is operated. Then, the interference information is subtracted from the read information of the target address.
According to a method for reading information of the present invention, the interference information generated by the addresses adjacent to the target address at its inner and outer peripheral sides are subtracted from the read information of the target address. With this arrangement, only the information recorded in the target address can be obtained from the information read from the optical disc. In this manner, even if the light beam is applied across the adjacent information recording layers in accordance with the increase in a storage density of the optical disc, the occurrence of crosstalk can be prevented.